The present invention relates to regulating the output voltage of a driver in a controller of a switch mode power converter to protect a power switch in the switch mode power converter.
A switch mode power converter—commonly used in low power AC-DC power supplies—includes a power switch, and a controller that controls the operation of the power switch. The power switch frequently has a specified maximum rated control voltage for safe and reliable operation. A control voltage, provided to the power switch, that exceeds the specified maximum rated voltage can damage or otherwise detrimentally affect the reliability of the power switch. Accordingly, to ensure safety and reliability of the power switch, the control voltage provided to the power switch of a switch-mode power converter needs to be limited to a value below the maximum rated control voltage.
Conventionally, a zener diode connected between the control terminal of the power switch and a voltage ground serves to limit the control voltage of the power switch to a value corresponding to a zener breakdown voltage, set to be lower than the maximum rated control voltage of the switch. However, at high operating control voltages, the zener diode, while limiting the control voltage to the zener breakdown voltage value, sinks large currents and contributes to power loss and operating inefficiency.